The answer & explanation for this question is given in the attachment below.
Answer:
2.97795 Hz
Explanation:
v = Speed of sound in air = 343 m/s
= Relative speed between the speakers and the student = 1.12 m/s
= Actual frequency of sound = 456 Hz
Frequency of sound heard as the student moves away from one speaker

Frequency of sound heard as the student moves closer to the other speaker

The difference in the frequencies is

The student hears 2.97795 Hz
never seen one although i guess the elegant answer is D) none of the mentioned posibilities